1. Field of the Invention
This invention relates control of a powertrain in an motor vehicle. More particularly it pertains to determining incipient positive torque in a powertrain, i.e., the threshold of a power-on condition.
2. Description of the Prior Art
The powertrain of a motor vehicle is tested according to a procedure defined by the federal government for compliance with governmental standards including conformance with onboard diagnostic capability (the OBD II test standard) and for other system diagnostics purposes. During execution of the federal test procedure, it is necessary to determine the torque produced by the engine of the powertrain. Conventionally, this torque magnitude is determined from a calibratable scalar value inferred by mapping engine torque magnitudes conforming to a range of engine parameters including throttle position, engine speed, MAP, temperature, etc. Preferably the engine torque determined in this way should be sufficiently high in order for the OBD II test to be conducted. However, variations in the vehicle weight, the gear ratio of the axle and performance variations associated with the service life of the powertrain affect the power-on threshold point, and in that way influence whether the calibrated scalar torque estimate is sufficiently high to permit federal testing to occur.
It is preferable to know precisely the threshold of the power-on condition rather than to arbitrarily estimate or guess a conservatively high torque magnitude. For example, when a fairly highly conservative torque magnitude is assumed for the threshold of the power-on condition, a large portion of the operating range of the federal test procedure can fail to run.
It is preferable that a control of a powertrain be capable of determining precisely the onset of a power-on condition, and that the control adapt to variations in vehicle gross weight, axle ratio, and the effects of service life and other vehicle-to-vehicle variations that influence the threshold of the power-on condition.
The federal test procedure requires that the onboard diagnostic system demonstrate its ability to detect a failure and to produce an accurate indication thereof to a vehicle operator. If the diagnostic system fails to detect and indicate the failure, the vehicle is determined to be non-compliant with a federal onboard diagnostic standard.
Typically the calculation of inferred torque into and out of the automatic transmission is not accurate at low torque levels due to vehicle variations and mapping inaccuracies. Since many of the functional tests used for OBDII diagnostics require a power-on indication to run, proper power-on indication is crucial, especially when running the federal test procedure drive cycle for OBDII compliance, which tends to run at a fairly low torque level.